Field of the Invention
The present invention relates to an electron microscope.
Description of Related Art
In an electron microscope such as a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), the most power consuming components are electron lenses. In order to achieve power saving in an electron microscope, it is desirable to deactivate the electron lenses when the microscope is not in use.
Generally, in an electron microscope, the interior of the electron optical column is evacuated by a sputter ion pump, while the interior of the detection chamber (camera chamber) is pumped down by an oil diffusion pump or a turbomolecular pump. Furthermore, an electron microscope is equipped with a sample contamination preventive device to maintain the degree of vacuum in the electron optical column and to prevent contamination of the sample. For example, JP-A-2002-203505 discloses an electron microscope equipped with a sample contamination preventive device (cooling device) for preventing adsorption of contaminants onto the surface of the sample by surrounding the outer periphery of the sample with cryogenically cooled fins and causing the contaminants (such as hydrocarbon molecules) causing contamination of the sample to be adsorbed onto the fins. The fins of the sample contamination preventive device are in thermal contact with a refrigerant tank. This tank is filled with a cryogenic liquid, such as liquid nitrogen or liquid helium, whereby the fins are cooled.
In the sample contamination preventive device, the cryogenic liquid filled in the refrigerant tank evaporates with the elapse of time. Finally, the liquid will disappear, whereupon the temperature of the fins rises rapidly. Gaseous molecules adsorbed on the fins are released in large quantities. This rapidly impairs the degree of vacuum inside the electron optical column. Consequently, the ion sputter pump evacuating the interior of the electron optical column may be damaged and made inoperable. In some cases, the ion sputter pump is destroyed.
Therefore, the user has had to perform manipulations to return the temperature of the fins to room temperature or higher after performing observation and analysis with the electron microscope while using the sample contamination preventive device.